An image photographed by a digital camera is generally stored as a file in an auxiliary storage device such as a CF (Compact Flash® memory) mounted in the digital camera. In order to capture the image, the digital camera is generally connected to a computer, a host application is activated in the computer, and the image is transferred.
In general, an application displays reduced images (thumbnail images) as a list of images stored in the auxiliary storage device of the digital camera. The user selects a desired one of the thumbnail images to capture an image file corresponding to the selected thumbnail image into the computer. The image file is displayed on the display screen of the computer or saved in the auxiliary storage device of the computer.
According to an image file format “Exif-JPEG”, which is generally employed in digital cameras, thumbnail images are stored in the same image file as that of main image data. In the above case, when a list is displayed, an area containing thumbnail image data out of the image file is transferred from the digital camera to the computer, and the entire image file need not be transferred to the computer. Hence, the processing speed is much higher than that in a case where the entire file is transferred to display thumbnail images.
For example, Japanese Patent Laid-Open No. 10-084473 discloses the following technique. That is, the transmitting side creates reduced images by reducing stored original images, and transmits image data of the reduced images to the receiving side. The receiving side displays a list of the received reduced images. Image data of original images corresponding to one or a plurality of reduced images selected from the list are transmitted from the transmitting side to the receiving side.
Recently, as the auxiliary storage devices mounted in a digital camera increase in capacity, the number of image files stored in the auxiliary storage device also increases. Transfer of only reduced images takes a long time when the reduced images of all images stored in the auxiliary storage device are transferred. A long transfer time degrades usability in, e.g., displaying a list of thumbnail images.